1. Field of the Invention
This invention relates to a construction to tightly seal fluid.
2. Description of the Related Art
In various fluid systems, various sealing materials are used on mutual connecting portions of fluid apparatuses and connecting portions of pipings. However, various apparatuses, becoming highly accurate and having high functions, are used under harsh circumstances for sealing material of rubber and synthetic resin difficult to be applied because of requirements of heat resistance, plasma resistance, and radical resistance. Further, supplied gas has become required to be highly pure with extremely low impurity level in which the above-mentioned sealing material of rubber and synthetic resin is not appropriate.
So the applicants of the present invention proposed a metal seal with torsional elastic deformation to seal two mutually parallel flat faces by metal touch as to correspond to the above-described harsh requirements (refer to Japanese patent No. 4091373, for example).
However, this metal seal may be difficult to attach and may drop out in attachment work. Especially, the metal seal tends to drop when attached toward a vertical face and a ceiling face. So, various holding devices for drop prevention are conventionally proposed (refer to Japanese patent provisional publication No. H10-209312, for example).
However, the conventional holding devices for drop prevention have the following problems.
(i) Although the devices are applicable when the metal seal is deformed by simple compression, it is quite difficult to certainly and stably hold the metal seal torsionally and elastically deformed.
(ii) Although the devices are applicable when the metal seal is deformed by simple compression, the torsional elastic deformation of the metal seal is impeded in the case of the metal seal torsionally and elastically deformed, and the metal seal does not function sufficiently.
(iii) When a holding plate for the metal seal with torsional elastic deformation is provided, dimensions of a sealing groove are different from that of conventional products in many cases, and design of joint main body must be changed.
(iv) The holding plate is also deformed along with the deformation of the torsional elastic deformation of the metal seal, the holding plate interferes with corresponding flat faces and generates abnormalities in fastening load, or sealing ability is reduced and corresponding flat faces are damaged.
(v) A large hitching groove portion is required as in the metal ring having a C-shaped cross section described in Japanese patent provisional publication No. H10-209312.
It is therefore an object of the present invention to provide a tight-seal construction with which the conventional problems are solved, dropping of the metal seal with torsional elastic deformation for sealing can be stably and certainly prevented by a simple and compact holding plate, conventional dimensions of sealing groove can be used without change, corresponding flat faces are not damaged, and fastening load can be held within an appropriate range.